A form of chain-growth polymerization, a ring-opening polymerization process, uses part of a polymer as a reactive center and joins monomers to form a larger polymer chain through propagation. An initiator reacts with a monomer to form an intermediate compound capable of linking successively with a large number of other monomers into a polymeric compound. The initiator can affect the polymerization process, such as initiation rate and polydispersity.